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88 Camry: Intermittent Alternator with Battery, Lights, and Brake Warning Lights

Hello I've got an 88 Camry, 4 cylinders, 230k mi. It runs really well except for this alternator problem which has confounded me. The car will run fine for anywhere from 1 minute to 2 or 3 hours with the alternator on, then the Battery, Lights, and Brake Warning lights all come on simultaneously. Then the car will run off battery and no alternator for a while before going back to normal. I can't connect the intermittentness with anything: it's TOTALLY random. Sometimes the car will start with the alternator working, sometimes it won't. If I leave it for a minute and start it up again sometimes the alternator works.

So I took the alternator into the local winchester auto and they bench tested it... as much as they wanted to sell me a new one, it was fine. My own inspection reveals healthy brushes and bearings.

The indicator lights and the intermittentness of it lead me to believe that it's a short circuit. I'm not an expert with electricity, but I've got a multi meter and more or less now how to use it. My haynes manual told me that if I put the multimeter between the negative battery cable and the negative battery post while the car is turned off, there should be no voltage. There is consistantly 11.5 (my poor battery). So I pulled out every fuse, trying to get the voltage to stop. Nothing. Does anybody have any advice or resources on how to troubleshoot this beast?

Please respond by post rather than email

Thanks Dub

Reply to
dub
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Have you checked the cable from the alternator to the battery?

Reply to
badgolferman

"dub" wrote: snip

Are you SURE that your manual says THAT?..You're to remove the negative terminal from your battery then measure the 'voltage' between that terminal and the negative battery terminal?

This makes no sense because if there's ANYTHING drawing power (such as the radio, clock, computer or any number of things that are normally connected) then you WILL read some voltage...it's perfectly normal to see some voltage here because there's always some light loads connected.

This is how you check the 'current' draw from your battery when not running...is it possible that they meant this?...the more that I think about this the more I'm convinced that that's what they meant. You need to select 'current' on your meter, not 'volts'... Does that manual say what current you should see?...I don't remember but some small value...ask Ray...

Reply to
Gord Beaman

The voltage between the negative battery cable and negative battery post should always be zero, whether the car is running or not. Remember, the negative battery cable is connected to vehicle ground. Likewise, the voltage between the positive terminal and positive cable will also be zero.

Voltage is potential - the difference between 2 points.

Current should be on the order of 15 milliamps with the car turned off. Are you sure you're not measuring at 11.5 milliamps?

The voltage between the positive battery cable or post and the negative one should be somewhere between 11.5 and 12 with the car off and up to 14 volts with the car running and the alternator functioning.

If you're getting 11.5 volts between the negative battery terminal and cable, the polarity on the battery is somehow reversed or the car's ground is somehow being energized. More likely, you are measuring something incorrectly.

The alternator needs power to produce power - make sure the wire is not loose, chafed, or stretched. Check the voltage regulator while you're at it.

Reply to
Ray O

Yes...providing that there's a good connection there...

Yes, but you must disconnect the negative terminal from the negative battery post first, then measure the current between them...Ray says max of 15 mA.

And for chrissakes don't test from the positive to the negative post with your meter on 'current'...you'll fry the fuse in your meter (or your meter itself)

Jeez...I had ASSUMED that they meant "disconnect the neg terminal from the neg battery post THEN check between that terminal and the neg post" for current...guess we'd better get some confirmation here...

Reply to
Gord Beaman

But... If you disconnect a cable from the battery post, there is not connection. If you're measuring voltage between a disconnected cable and post, the quality of the connection depends on how the meter leads are touching the post and cable.

Reply to
Ray O

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